<select name="sexo" id="sexo">
  <option value=""></option>
  <option value="I" <? if($sexoSeleccionado == "I") echo "SELECTED";?>>Indistinto</option>
  <option value="M" <? if($sexoSeleccionado == "M") echo "SELECTED";?>>Masculino</option>
  <option value="F" <? if($sexoSeleccionado == "F") echo "SELECTED";?>>Femenino</option>
</select>
